(1) Field of the Invention
The present invention relates to a transmission for use in a lawn mower or an agricultural tractor to provide plural backward and forward speeds.
(2) Description of the Prior Art
In a known transmission, a differential case is attached through bearings to mounting bosses defined on inside walls of a transmission case (see Japanese Patent Publication Kokai No. 63-46955 for example).
Further, a disk type stepless transmission is known, which is capable of backward and forward drive switching and of providing a plurality of speeds in either of the backward and forward drive states (see Japanese Patent Publication Kokai No. 63-84450 for example).
In the former, the transmission case must include the mounting bosses on inside walls thereof for attaching the differential case. These additions render the transmission case complicated, and adds to difficulties in the manufacture thereof and in the arrangement of its components.
The latter has the advantage of enabling backward and forward drive switching and stepless change speed in either of the backward and forward drive states, which are effected by a single stepless change speed device. In practice, however, a large drive disk and a large driven disk are required to avoid a drastic reduction in the transmission efficiency. The whole construction is thus inevitably large despite the feature that the single change speed device is used for both the backward and forward drive switching and the change speed. Even though the disks are enlarged to improve the transmission efficiency, this stepless transmission, because its drive transmission is effected by a pressure contact between the drive and driven disks, cannot provide a higher transmission efficiency than a gear type transmission.